1. Field of the Invention
The present invention relates to a cathode ray tube and a method of manufacturing the same.
2. Description of the Related Art
The panel of a cathode ray tube is produced by molding molten glass. During the molding process, the surface of the panel becomes rough, so it is necessary to polish the surface of the panel before supplying it for use. In the process of production of a cathode ray tube, this polishing step accounts for 20 to 30 percent of the time and cost involved in making the panel. Therefore, rationalization of this polishing step is necessary in order to meet with demands for reductions in the cost of manufacturing cathode ray tubes.
The increasing size of cathode ray tubes and the increasing flatness of their panels have in addition been accompanied with thicker designs of their panels in order to secure their requisite anti-implosion performance. When panels are made thicker, however, their weight undesirably increases.
In view of this situation, there have been proposed the method of adhering functional glass to the surface of the panel by an adhesive (polypropylen glycol PPG laminate method) and the method of adhering a transparent functional film to the surface of the panel by an adhesive so that there are not that great demands on the precision of polishing of the panel surface and further the thickness can be kept thin.
In the former PPG laminate method, the final polishing of the panel is eliminated, but taping and other complicated steps are involved. The latter method is therefore considered more promising.
In both methods, however, there are problems with preventing charges from forming at the panel surface.
The following two methods are known for preventing charges. Each has its own problems, however.
The first method calls for spraying the face of the panel with an alcohol solution of silicon alkoxide in which has been dispersed a conductive filler such as indium tin oxide and tin antimony oxide, baking this at a relative high temperature (150.degree. to 200.degree. C.), and thereby forming a conductive layer on the surface of the panel. The conductive layer formed by this method is extremely difficult to salvage after baking when a defect is found in the coating. Further, when touched by the hand, it picks up fingerprints or other dirt and therefore causes a deterioration in the quality of the reproduced image. This dirt is also hard to remove by wiping with a dry or wet cloth etc.
The second method calls for adhering by an adhesive to the outer surface of the panel of a cathode ray tube a panel comprised of a sheet of glass molded to the radius of curvature of the outside of the panel and formed on its surface with an anti-reflection film comprised of a transparent conductive layer made of indium tin oxide etc. and multilayer optical thin film comprised of titanium dioxide, silicon dioxide, etc. This method is now being used for some cathode ray tubes, but has problems in terms of suitability for mass production and further increases the manufacturing costs.
Further, it has been considered to include the transparent conductive layer in the functional film adhered to the surface of the panel. Effective and simple means for grounding this conductive layer have been sought.